Self-locking nail



Patented Aug.. 9, 1938 UNITED sTATEs PATENT OFFICE 7 Claims. This invention relates to wire nails of the type in which the shank is surrounded by encircling.

barbs or flanges capable of making an interlock with the wood or other material in Which the nail is driven. Its object is to combine maximum holding power with a construction or formation which requires the least possible diminution of diameter at any point from the original diameter of the stock out of Which the nail is 10 made. In other words, the object comprises retention, in the greatest possible degree consistent with adequate looking power, of the original ltensile strength of the stock: and also comprises the object of keeping the cost and price of the nails as low as possible.

One particular and important use for which such nails are intended and adapted is to secure asbestos shingles, or other fire resistant slabs or strips of material prepared for the roof and wall coverings of buildings, to previously completed buildings over the old shingles or clapboards thereon. Re-covering an old building in this manner is much less expensive than the process involving preliminary removal of the old shingles or clapboards. It also has the practical4 advantage that such-weather protectivecapacity as uremains in the old shingles,`and their heat insulating properties, are retained. But it is attended by diiiiculty due to the fact that the old shingles are usually more or less warped and curled from Weathering. The force applied in driving the nails to hold the new covering shingles flattens the old shingles. But the latter are under continual tension tending to bring them back to the curled shape. This exerts an outward pressure on the overlying shingles tending to withdraw the nails, which is augmented by Wetting and drying of the old shingles, for thecover shingles cannot be laid so perfectly water-tight as to prevent any penetration of water and moisture in driving rains or damp Weather. Then the old and weatherbeaten shingles and clapboards are more brittle than fresh wood and have comparatively little holding power. Thus smooth nails soon become loose, if they do not fall out altogether, even though long enough to penetrate to some extent into the boards of the roof or sides of the building, and leave the cover shingles so loose that they rattle in the wind and may be blown off by a high wind. Ability to make a secure interlock with wood of suflicient gripping power is therefore essential in nails provided for this purpose.

Such nails must also be substantially noncorrodible. They are preferably made of nonferrous metal such as bronze or brass, or nonrusting alloys of iron. Such metals and alloys are relatively very costly in comparison with 'the mild steel of which ordinary wire and cut nails -are made. Hen'ce the avoidance of waste in manufacture and the provision of suificient length, strength, holding power and stiffness with the least possible weight are important factors of the problem.

By the present invention I have produced a nail having stronger looking and holding qualities than any other nail of comparable dimensions, of which I have knowledge, and in which the strength and stiffness are more nearly equal 15 to the strength and stiifness of the original stock before the formation of the looking barbs. The nails embodying the invention have the characteristics hereinafter described with reference to the'drawing. i

In the drawing,-

Fig. ll is'a side elevation of a commercial nail embodying the invention drawn on a greatly enlarged scale. with a substantially accurate representation of the proportions between the zones 25 of different diameters;

Fig. 2 is a sectional view of a fragment of the nail taken on line 2-2 of Fig. l and shown on a scale four times that of Fig. 1.

The nail thus represented is made of Wire, 30 preferably hard drawn brass or bronze wire so as to be non-rusting. It is formed with protruding encircling flanges a, a', b, b', c, c', etc. arranged in pairs with intermediate grooves. As a convenient descriptive term, such encircling 35 fianges are called barbs; and to distinguish the members of each pair from one another, those shown at a, b, c, etc. are called primary barbs and those represented by a', b', c' are called secondary barbs or shoulders. Their function 40 and effect is to interlock with the fibers of word or other materials into which the nail may ce driven and to resist withdrawal.

The primary barb of each pair is of larger diameter and more acute angularity in profile than the secondary barb. Its side which faces toward the head 3 of'the nailA is formed with a face 4 which is substantially perpendicular to the axis of the nail, at least in its outermost part. Between the primary and secondary barbs of each 5o pair is a shallow groove E, while between the secondary b'arb of one pair and the primary barb of the next is' a deeper groove G, the side 'l of which toward the adjacent secondary barb is vconical. The bottom of such groove is preferobtuse angle; although the invention is not limited to this detail. i

An important factor is that the barbs, or at least the primary barbs, and usually also the secondary barbs, are of larger diameter than the original stock from which the nails are-'made while the grooves O are of only sli'ghtly 'smaller diameter in their deepest parts. The proportional diameter of the original stock is shown in the drawing by the ungrooved portion I of the nail adjacent to its head. i

The formation above described is given by rolling the nail blanks under pressure between suitably formed dies in such manner that the metal of the shank is displaced and caused to flow into contours substantially as shown. .Such contours enable the metal to be displaced outwardly in the primary barbs farenough to provide looking shoulders of adequate radial extent and area for making a 'secure interlock, and. with so small a quantity of metal outside of the original diameter of the stock that it is furnished by displacement of only a small amount of metal from within the original diameter. In other words, this character of barb formation provides a sufllciency oflocking projection with the minimum of reduction in diameter st the narrowest zone.

By way of illustration, but without intending any limitation to specific dimensions, I will describe the details of one commercial nail which I have produced. This nail is made from wire .083" in diameter. It is formed with 24 barb pairs per inch of length and in lengths from l" to 2" or more. The metal is offset by suitable pressure treatment to a diameter at the periphery of the primary barbs of .096 and withI reduction of diameter at the deepest parts of the grooves to .O76. The diameter ofthe secondary barbs and the depth of the grooves 5 between the barbs of each pair are of minor importance. However, in this illustration the secondary barbs are approximately .090' in diameter and the grooves I at their bottoms are of approximately the same diameter as the original stock. Ex-

pressed in proportional terms, the protrusion of' the primary barbs from the original diameter of the stock is very nearly twice as great as the sinking of the principal grooves within the original diameter. In nails made from stock of .different diameters, different materials, different pitch (or spacing) of barbs, and different contours of grooves, the proportional enlargement and reduction in different parts may be greater or less than this, wherefore I desire not to limit the protection claimed to the specific values above stated.

The formation of wide looking shoulders by flowing of metal and with a less reduction of diameter at the grooves than enlargement at the primary barbs, is an important factor in the production of strongly looking nails from expensive metal without waste of material and with minimum sacriilce of strength and stiffness. In order to provide as many nails as possible to the pound; wire of the least diameter which would provide adequate stiffness is used; hence the importance of reducing the original diameter as little as possible in forming the barbs.

The dual or duplex barb formation is useful both for the assistance it aifords in driving the nail and for the additional holding power which it furnishes. I believe the probable reason for this is that, in the course of driving the nail, the conical surface in-advance of each secondary barb gradually crowds the ilbers .of the wood apart to a distance less than the diameter of the primary barb and allows a partial recovery or spring back of the flbers before passing the primary barb. Possibly also the primary barbs, which are extremely thin at their circumference, yield when advancing and recover when fully driven. When the nail rests at its limit of penetration, the bers back of the secondary barbs produce a holding effect additional to that of the fibers back of the primary barbs, augmenting the looking Veffect of the latter..

This augmented effect is obtained without increasing the number of primary barbs or shortening the distance between them. The nails here illustrated have 24 pairs of barbs to the inch of length, equally spaced. This is practically as large a number (conversely, as close a spacing) as is feasible to make. While it would be possible to locate single barbs closer together than 24 to the inch, it would not be possible to provide as many as 48 to the inch and still make wide enough shoulders to give the desired depth of interlock, with spaceenough between them for entrance of the woodfibers to the full interlocking depth. There is also an outer limit of interlooking overlap between barbs. and enveloping wood beyond which it is not possible to go without breakage of fibers or straining of the wood too far to spring back behind the barbs. I have found by experience that the spacing and proportions of the barbs as here shown give remarkable results in holding power with minimum injury to the wood when the nail is driven. The peculiar and novel formation here shown not only provides the strength and security due to such spacing and proportions, but it adds the strength of interlock due to the secondary barbs, which is an entirely new source of strength. And this construction is obtained by displacement of the metal in stock of minimum diameter without appreciable sacrifice of tensile strength or stiifness and with no waste of metal' such as would occur if the barbs were made by cutting from a larger wire or rod. The fillets at the bottom of the grooves give strength to resist bending and fracturev of the nail in the zones of least diameter.

The'same principles may be embodied in nails of any material, corrodible or not, where the circumstances of use permit employment of corrodible materials; and may be embodied also in dowels adapted to be driven into previously prepared holes of less diameter than the barbs, in wood or other materials. For instance, such a dowel is well adapted to secure the lifts of built up heels together, for the barbs and tensile strength of the dowel furnlsh a bond additional to that afforded by cement which may be used. In short, the explanatory description of a use for which a specic embodiment of the invention is designed, is not to be construed as a limitation of the scope for which protection is claimed.

What I claim and desire to secure by Letters Patent is:

' 1. A self-looking nail having barbs or flanges surrounding its shank and arranged in pairs, of which the barb more remote'from the entering end of the nail has a larger diameter and a more acute angle in proflle than the other barb of 'the A :alsanea same pair, and the distance between the barbs of each pair is shorter than the distance between the adjacent barbs of successive pairs.

2. A self-looking nail having holding barbs or flanges arranged in pairs spaced apart from one another, corresponding barbs of each pair being substantially equal in diameter, the barb of each pair nearer to the head end of the nail having a face at the side toward such head end which is substantially perpendicular to the length dimension of the nail, and the other barb of the pair having a conicalformation on the side toward the entering end of the nail.

3. A self-looking nail having holding barba or ilanges arranged in pairs spaced apart from one another, the barb of each pair nearer to the head end of the naii having a face at the side toward such head end which is substantially perpendicular to the length dimension of the nail, and the other barb of the -pair having a conical formation on the side toward the entering end of the nail, the barbs of the pair being separated by an indentation of less depth than the indentation between adjacent pairs;

4. A self-looking nail having holding barbs or flanges arranged in pairs. each consisting of a primary barb and a secondary barb in tandem arrangement, the barbs of each pair being spaced from one another by a distance less than the distance between the secondary barb of one pair and the primary barb of the next pair, there being a shallow groove between the barba of each pair and a deeper groove between successive pairs of A having a substantially plane side substantially barba. the latter groove having a conical side which forms one side of the secondary barb. and

perpendicuiar to the axis of the nail which forms the locking shoulder of a primary barb, and said sides being joined by a concave flllet.

5. A self-looking nail comprising a wire shank having indented encircling grooves spaced apart at substantially equal intervals, and the material between such grooves' being in extruded formation comprising an encircling primary and a secondary barb each of larger diameter than the original wire. the primary barb being of larger diameter than the secondary barb and having an abrupt shoulder at the side toward the head end of the nail, and there being a relatively shallow 6. A self-looking nail comprising a `wire shank having indented encircling grooves spaced apart at substantially equal intervals, and the material between such groovesv being in extruded formation comprising an encircling primary and secondary barb each of larger diameter than the original wire, the primary barb being of larger diameter than the secondary barb and having an abrupt shoulder at the side toward the head end of the nail, the face of 'such shoulder being Joined ona curve with the bottom of the adjacent groove, and the secondary barb being separated by a relatively shallow groove from the primary barb and having a conical face at the side opposite to the last narned groove.

7. A self-looking nail .havingbarbs or flanges surrounding its shank and arranged in pairs. of

which the barb more remote from the point of the nail, in each pair, ,is larger in diameter than the other barb of the same pair and is substantially equal in diameter to the corresponding barbs of other pairs. 1

KERMAN .maas s'romr.

groove between the primary and secondary barbs. 

